Certain types of composite structures include reinforcing elements to improve the strength and stiffness characteristics of the composite structure. For example, the wings of an aircraft may include composite skin panels which may be stiffened with composite stiffeners. The composite stiffeners may be located on an inner side of the composite skin panel and may increase the out-of-plane bending stiffness of the composite wing skin.
Conventional methods of forming stiffened composite skin panels may involve laying up composite plies on a skin layup tool to form an uncured composite skin. One or more composite stiffeners may then be individually laid up or mounted on the composite skin. The composite assembly may be vacuum-bagged and compaction pressure may be applied to debulk the composite assembly. Heat may also be applied to cure the composite assembly and establish the outer mold line surface finish of the composite skin. Unfortunately, the conventional method of laying up a composite skin and then individually installing composite stiffeners results in a relatively long process flow time for manufacturing a stiffened composite skin panel.
In attempts to reduce the process flow time, composite stiffeners may be separately laid up on stiffener tooling to form a stiffener assembly. A skin layup tool containing an uncured composite skin may be applied to the stiffener assembly to form a skin-stiffener assembly which may be vacuum-bagged and positioned in an oven or autoclave for curing to produce a stiffened composite skin panel. Unfortunately, the installation of the composite skin onto the stiffener assembly may require the use of a crane for lifting and positioning the skin layup tool which may present challenges in maintaining the safety of the workplace in addition to challenges in accurately aligning the composite skin with the composite stiffeners.
Furthermore, the skin layup tool must be relatively stiff to avoid distorting the contour of the outer mold line on the layup surface during layup of the composite skin. Unfortunately, a relatively stiff skin layup tool may present challenges in applying uniform compaction pressure to the composite skin during debulking. In addition, a relatively stiff skin layup tool may have a relatively high mass which may result in the application of excessive compaction pressure onto the composite skin, the composite stiffeners, and the stiffener tooling. Furthermore, the relatively high mass of a stiff skin layup tool may increase the amount of time required for heating up the composite assembly to the cure temperature and cool down to ambient temperature after the composite assembly is cured.
As can be seen, there exists a need in the art for system and method for manufacturing a stiffened composite skin panel that allows for layup of the composite skin in parallel with the layup of the composite stiffeners, and which additionally allows for the application of uniform compaction pressure to the composite skin during debulking while avoiding the need for a crane for lifting and positioning the skin layup tool.